This invention relates to a method of labeling containers with polymeric materials particularly adapted for use as labels in the post mold labeling of plastic, glass or metal containers or surfaces. More particularly, the present invention relates to the use of particular low density polymeric film substrates adapted for printing that may also have a hydrophilic surface layer for use as labels in post mold labeling applications using conventional wet applied water based labeling equipment and solutions typically used for the application of paper labels. In another aspect the invention relates to such labels which possess the beneficial properties of the known plastic label substrates, but which are able to be applied on conventional post mold paper labeling equipment using wet applied water based solutions comprising water, water blended with a selected catalyst, adhesives or adhesives blended with a selected catalyst and are adapted to facilitate the recycling process when the labels are applied to certain types of containers.
Plastic and glass containers or bottles are prevalent in a wide variety of shapes and sizes for holding many different types of materials such as detergents, chemicals, motor oil, beer, etc. These containers are glass or plastic (mono or multi layers) of polyethylene, polypropylene, polyester or vinyl along with other specialty blends for specific barrier and product resistance performance. Generally such containers are provided with a label which designates the trade name of the product and may contain other information as well. The early art which still is prevalent today employed the use of labels manufactured from paper substrates that were applied with a water based adhesive. Subsequently, dry pressure sensitive self adhesives and in mold labels manufactured from paper have been and continue to be used. The shortcomings of paper labels with regard to tearing, wrinkling, creasing and the like due to age and moisture, or due to a lack of deformability when applied to a deformable plastic substrate have been well documented in the labeling industry. Because of this and the need to produce recyclable plastic containers, over the years a great deal of effort has been expended to develop container decoration techniques and durable polymeric film substrates or face stocks which would overcome these shortcomings. Film facestocks for container decoration which have resulted from these efforts can be applied to glass and plastic containers as self adhesive pressure sensitive labels as described in the prior art. The use of self adhesive paper and film xe2x80x9cpressure sensitive adhesivexe2x80x9d (PSA) labels that have been preprinted and supported on a release liner is not a cost effective option because of the added cost of the release liner used to support and render processable the self adhesive face stock. The cost of this type of structure combined with the added cost of disposal of the liner does not make pressure sensitive labeling a desirable option from an economic or environmental standpoint. In addition, new capital intensive labeling equipment is required to transition from wet applied Post Mold Labels (PML) to self adhesive PSA labels plus the effect of a new process on an existing packaging line in terms of learning cure and experience. Cut PML labeling equipment typically will run to six times the speed of a PSA labeling system.
Another film face stock labeling technique that has evolved is the use of heat activated in-mold labels as described in the prior art where a preprinted plastic label with a heat activated adhesive on the back of the label is placed in the mold before the molten plastic resin is injected or blown into the mold cavity at elevated temperature and pressure which activates the adhesive and fuses the label substrate to the container in-mold. The use of film based in-mold label substrates presents a more cost effective alternative then self adhesive pressure sensitive labels in terms of substrate cost but as this technology has progressed, it has been found that productivity is impacted by the label feeding step into the mold which is performed in a complex, continuous and rapid manner which can result in large amounts of scrap material. Also, the initial capital investment required to tool up for a container specific in-mold label process for new molds and the complex electromechanical maintenance intensive feeding devices is significant. Another detriment for this process is the potential inventory carrying costs for varieties of labeled containers that come into play with predecorated containers such as in-mold for those who would choose to apply the label immediately pre or post filled.
Post mold decoration of glass and plastic containers in the current art can also be accomplished by direct screen printing on the container. Direct screen printing on the container is not a cost effective process and also presents the aforementioned inventory problems along with added cost for freight to and from a screen printer. The graphical possibilities for label copy are limited in terms of cost and quality with this technique. Commodity products can not support the cost of this labeling technique.
Another post mold technique that has been popular is the xe2x80x9cThermagexe2x80x9d process. This process transfers a reverse printed image from a transfer release paper under temperature and pressure to produce decorated containers. The xe2x80x9cThermagexe2x80x9d technique of transferring a reverse printed image is costly because of transfer release paper costs and presents the same disposal problems and costs with the transfer sheet as occurs with the aforementioned release liner used in conjunction with self adhesive labels.
Other techniques for labeling various plastic and glass containers with preprinted paper or film label substrates include the use of hot melt adhesives which are applied to the label substrate or container in a molten state with container and substrate subsequently married while the hot melt is molten. When the hot melt adhesive cools, it sets up and bonds the label substrate to the container.
This technology requires the use of sophisticated melting and application equipment that must be operated, cleaned and maintained at elevated temperatures. This technology works well with complete 360 degree wrap around labels but has not evolved to the point to allow consistent labeling of a die cut or square cut xe2x80x9cpatch labelxe2x80x9d with less than 360 degree wrap. Affixing a patch label to an area on a container with 100% or patterned adhesive application using hot melt adhesives has not been commercially perfected. Complete wrap around hot melt applied labels where one end of the label is affixed to the container while the other end is wrapped around the container greater than 360 degrees to form a glue lap where the trailing edge is affixed with hot melt to the leading edge of the label substrate is proven hot melt label application technology that works well for film and paper label substrates. This labeling technique does not fit for applying patch labels on individually labeled panels of containers such a rectangular oil, contoured detergent or beer containers where a neck and front label only are applied. Another drawback is the added cost for label substrate when this technique is used since more label substrate is required because of the 100% wrap around.
Lastly, and still one of the most prevalent labeling techniques is the application of paper based cut patch labels to glass and plastic containers using natural and synthetic laminating adhesives such as BL300 produced by Henkel Adhesives or OC353-20 produced by O.C. Adhesives Corp. which are known to the art. This is a safe (water based) proven technology that has grown and been employed for many years and consequently there are many existing machines that have been installed for this type of labeling technique such as from Krones, Neutraubling, Germany that run precut patch labels or Koyo, Japan which runs roll stock that is cut into a rectangular or square patch label on the labeling machine to the label size. The cut label techniques and associated adhesives work well with paper based substrates applied to glass or plastic containers because the wet adhesive wicks (absorbs) into the paper substrate from the applicator roll, pad or pallet which breathes and allows the moisture from the water carrier to be absorbed by and dry thru the paper base.
This technique obviously will not work with non-porous polymeric label substrates as the adhesive cannot dry thru (wick into) the polymeric substrate. The adhesive and polymeric label substrate must be chosen to have initial tack and adhesive transfer to the label. Typically, wet applied cut label machines work where glued pallets remove the label out of the label holding magazine while simultaneously gluing the back side of the label. This is accomplished by applying a thin glue film to the pallet which is then pressed in intimate contact against the first label in the stack. After its removal, the label sticks on the entire glued area of the pallet until transferred to a xe2x80x9cgripperxe2x80x9d cylinder and removed from the pallet. The gripper cylinder then transfers the label to the container to be labeled. The various machine designs and techniques are well known within the labeling industry and to those skilled in the art. The xe2x80x9cKrones Manual Of Labeling Technologyxe2x80x9d by Hermann Kronseder dated December 1978, is hereby incorporated by reference.
Attempts have been made to use polymeric substrates with high moisture vapor transmission rates (MVTR) such as films with micro perforations for drying of the water trapped between the label and the container and high solids tacky or pressure sensitive adhesive for good wet tack on conventional wet water based labeling equipment with little success. The high solids tacky adhesive required to stick to the polymeric substrate causes machining problems by gumming up the adhesive application system and creates cleanup issues. The high MVTR substrates also did not have good wet tack with existing commercially available adhesives that would machine without problems and did not dry rapidly enough making the labels prone to xe2x80x9cswimmingxe2x80x9d or moving from the desired application area during down stream processing. The micro perforated materials allow adhesive to ooze thru the label contaminating the label surface ruining the graphics and making the label sticky. In addition, many of the current paper adhesives do not wet out and apply uniformly to non hydrophilic surfaces with the crude adhesive metering and application systems currently in use on existing paper labeling machinery. Without uniform application, wet out and wet tack, it will be impossible to successfully apply a polymeric label because of adhesive and application imperfections.
When plastic or glass containers are recycled, the first step involves cleaning, then label removal and separation of the labels from the used containers. When polymer labels are removed, they are sometimes difficult to separate from the liquid/label/container mixture that is formed during the recycling process if the density of the polymer label is high enough that it will not readily separate and float on the surface of the liquid that is used for label removal. The applicant has discovered that if the polymer stock for the label is a material having fine micro voids and a density that is substantially lower than the label removal fluid, not only will the labels be easily separated from the container/label/liquid mixture because they float on the surface of the label removal liquid which simplifies the recovery of the glass or plastic container for recycling, but the polymeric labels will also function well in wet glue PML labeling.
Accordingly, it is an object of the invention to provide a polymeric label particularly adapted for use in post mold wet applied labeling of polymeric and glass containers that would readily feed from the label magazine or gripper, adhere with sufficient tack without moving through post labeling handling and processing including but not limited to conveying, filling, case packing and palletizing and is adapted to recycling.
It is also an object of the invention to provide a polymeric label particularly adapted for use in post mold wet applied labeling of polymeric and glass containers that would have sufficient wet tack and affinity for water, a water based solution or adhesive used to allow for transfer of the wet water based adhesive to the polymeric label substrate from the applicator roll(s), pad(s) or pallet(s) of the labeling machine and is adapted to recycling.
It is also an object of the invention to provide a polymeric label for use in post mold wet applied labeling of polymeric and glass containers that would have a coefficient of expansion or contraction under the conditions which the container sees which is the same or compatible with that of the polymeric resin, glass or metal from which the container is made so that expansion and contraction of the container will not wrinkle or otherwise affect the integrity of the label and is adapted to recycling.
It is also an object of the invention to provide a polymeric label for use in wet applied post mold labeling which would combine suitable properties of modulus of elasticity and flexibility and would not be degraded by handling and flexing of the subsequent container and is adapted to recycling.
In considering the performance or economic shortcomings of prior art materials, I have discovered a process by which a polymeric label may be applied to a glass, plastic or metal container or surface by means of a water based adhesive composition, said method comprising:
(a) selecting a polymeric label having a density of less than 0.9;
(b) applying a water based adhesive to said polymeric label to form a fastenable polymeric label;
(c) fastening said fastenable polymeric label to a glass, plastic or metal container or surface; and
(d) allowing said polymeric label to dry on said glass, plastic or metal surface or container.
The invention also provides a plastic metal or glass container having a polymer label comprising a low density polymer, a dried water based adhesive which affixes said polymer label to said container, wherein said polymer label contains a portion of said dried water based adhesive within said polymer.
The use of the low density micro-voided polymer film can allow portions of the water based adhesive to migrate into the film during the drying cycle to provide an enhanced bond between the polymeric label and the container surface and to also impart stiffness to the dried label on the container surface.
The preferred low density polymeric labels are made of polypropylene which is commercially available. The preferred density is 0.55 to 0.85, an especially preferred density is 0.6 to 0.75, as distinguished from the conventional polypropylene label stock which has a density above 0.9. These materials are sometimes referred to as cavitated, micro voided or foamed polypropylene. Other polymers which may be used include polyethylene, polyester, polystyrene, polycarbonate or compatibilized polymer blends.
It is preferred to utilize a hydrophilic material in conjunction with the low density polymeric label to allow for more rapid escape of water from the water based adhesive that is placed on the back of the low density polymeric label.
Hydrophilic materials are selected so that their thickness and modulus of elasticity when applied to a polymer film will result in a polymeric film facestock that will have hydrophilicity, absorbtivity, wet tack and drying properties that will permit the polymer film to be applied to polymeric or glass containers via water based wet labeling techniques on standard paper labeling equipment. The apparatus which is used to apply paper labels is well known to those in the art. The polymeric label substrate with the hydrophilic coating will demonstrate sufficient xe2x80x9cwet tackxe2x80x9d during the label application period and the label drying period to permit containers to be handled and processed. The polymeric film based facestock will provide a label with printability, chemical and dimensional stability, resistance to cracking, tearing, creasing, wrinkling or any other degradation of the sort experienced by paper labels due to physical or environmental extremes.
As used herein, the reference to xe2x80x9ca containerxe2x80x9d includes a surface of an object made of glass, plastic or metal, such a dishes, toys, beer bottles, building materials and the like.
Optionally, if a metalized coating of a thin metal film is deposited on the polymeric sheets or rolls, premium quality decorative labels with all of the advantages set forth above will be provided.
The hydrophilic component or blends containing the hydrophilic component will be applied in the present invention to the selected polymeric sheet in a continuous or patterned layer to provide the absorptive, wet tack and drying properties that are necessary to enable polymeric sheets to be successfully used as label substrates on polymeric or glass containers when applied with water based wet labeling techniques. The hydrophilic layer which may be applied by either a coating or an extrusion technique has the function of absorbing moisture to activate the layer, thus causing the hydrophilic layer to function as an adhesive without any additional adhesive or to absorb the moisture from an adhesive if used and to pass the moisture thru the hydrophilic layer and micro voided substrate to cause the polymer film to adhere to the glass, metal or plastic container and to set up rapidly and positively.
The choice of polymeric substrate for the label film will determine the rigidity, deformability or conformability, regrindability, printability and expansion or contraction characteristics required for application to the selected container without the problems associated with paper labels.
The term xe2x80x9cfilm facestockxe2x80x9d or xe2x80x9cpolymeric label substratexe2x80x9d as used herein should be taken for purposes of the present invention to refer to a monolayer, coextruded, coated or laminated material compatible in terms of rigidity, deformability or conformability, regrindability if a plastic container and expansion or contraction characteristics with the plastic, metal or glass container to be labeled. Similarly, the xe2x80x9chydrophilic layerxe2x80x9d previously mentioned has the properties of wet tack, absorbtivity, drying, sufficient adhesion to the polymeric label substrate and affinity and adhesion to the labeling adhesive if used in the wet or dry form.
It is contemplated that selected hydrophilic layers can be wet or remoistened without adhesive for use on a glass or plastic container or a water based adhesive can be used to affix the polymeric label substrate with the hydrophilic layer to the glass or polymeric container. For deformable containers, the adhesive if used, can be selected from those commercially available that are characterized by the ability to form a bond with the container and a hydrophilic layer such that when dry, the strength of the container wall-adhesive interface and the hydrophilic layer-adhesive interface and the cohesive strength of the adhesive itself are all greater than the forces required for deformation of the label.
As used herein and in the appended claims, the term xe2x80x9chydrophilicxe2x80x9d is used to describe materials or mixtures of materials which bind, pass or absorb water. The preferred xe2x80x9chydrophilicxe2x80x9d materials are those acrylic polymers which bind or absorb water. The especially preferred xe2x80x9chydrophilicxe2x80x9d material is DP6-6006, a sodium polyacrylate available from Ciba Specialties.
It is also an aspect of the present invention to use cross-linkable (reactive) components in the hydrophilic layer that can cure with a catalyst supplied in the hydrophilic layer, rewetting water or adhesive (if used) that will promote adhesion to the labeled container along with chemical and moisture resistance. Examples of cross-linkable materials include carboxylated synthetic resins. The catalyst can also be added to the adhesive which could have reactive components which would cure the adhesive and hydrophilic layer together. Examples of cross-linkable components include zirconium salts of mineral acids, polyfunctional aziridine, water soluble polyamide-epichlorohydrin material such as Polycup 172, zinc ammonium carbonate and the like which may be used at a level of 0.2-8% by weight of the adhesive composition.
The coated, extruded or coextruded hydrophilic layers can be defined as substances capable of combining two surfaces by the formation of a bond whether it is a moist hydrophilic layer to glass or polymer or a dry hydrophilic layer to a wet labeling adhesive which as an intermediate layer that bonds to both the hydrophilic layer and glass or polymer of the container when dry.
The use of the proper hydrophilic layer for a given polymeric labeling substrate and container to be labeled will have a direct effect on the speed which the labeling line can be run.
When considering the choice of the material which forms the hydrophilic layer, which may be applied by coating, coextrusion or extrusion, one must consider the label substrate, container to be labeled, labeling machinery, water or adhesive application technique and down stream processing requirements such as filling, conveying and packing. Generally a thickness of from 0.1 to 8 mils of the hydrophilic layer, when dried, may be employed on the polymeric film layer, depending on the particular hydrophilic material that is selected.
It is critical to the successful application of a hydrophilic polymeric film label to control how the water or water based adhesive is applied to the hydrophilic layer, how deposition (weight or thickness) is controlled and how the resultant combination with the container is pressed together. Generally, from 0.25 to 6 mils of water or water based adhesive is applied to the hydrophilic layer with 100% coverage of the label. If a grid or other pattern of adhesive is employed, then the overall amount of adhesive consumed is reduced. If a grid pattern is employed, the hydrophilic layer may be applied to be substantially in register with the adhesive layer. It will generally be possible to reduce the typical amount of adhesive applied to a label when using the hydrophilic layer of the invention to an amount which 20-80% of the amount that is typically employed for affixing paper labels to a surface. The choice of the hydrophilic layer and the type of label substrate and container to be adhered together, as discussed above, the plant processing conditions after labeling, storage requirements and the end use requirements that must be met such as high temperature resistance or ice proofness and the choice of an intermediate adhesive layer are important considerations. There are many more specific variables within these considerations all of which influence the formulation of the proper hydrophilic layer and adhesive (if used) for a specific application.
Mechanical adhesion is defined as the bonding between surfaces in which the adhesive holds the parts together by inter-locking action and actual physical penetration. Specific adhesion is the bonding between surfaces which are held together by molecular forces wherein the surfaces are non-porous and no penetration is possible.
These forces are related to the polarity and size of the molecules and the initial action in obtaining a bond when the hydrophilic surface is wet and a bond develops through molecular forces.
In mechanical as well as specific adhesion, the optional hydrophilic layer with optional intermediate adhesive layer must xe2x80x9cwetxe2x80x9d both surfaces completely or weak bonded areas will develop as it dries or xe2x80x9csetsxe2x80x9d resulting in a poor bond. Not only is wetting of the surfaces critical, penetration is also important. Penetration is important since most combinations of surfaces to be adhered together involve at least one porous or absorptive surface which controls the xe2x80x9csettingxe2x80x9d characteristics. To facilitate specific adhesion, wetting of the surface and penetration are critical for the hydrophilic layer or hydrophilic layer with intermediate adhesive which must be in a fluid state. For purposes of this invention, this is accomplished by applying water or water based adhesive to the selected hydrophilic layer which when applied to the container to be labeled brings the hydrophilic layer and container wall into intimate molecular contact. By using a wet hydrophilic layer or intermediate adhesive which also wets and penetrates the hydrophilic layer as well as the container surface, a fluid region is created that flows to cover the surface as completely as possible. This is critical to the invention where even an apparently smooth surface in reality is composed of a random network of hills and valleys. When the hydrophilic layer is in the wet condition, with or without adhesive, it serves as a wetting bridge to promote adhesion.
Various commercially available adhesives can be utilized to provide good adhesion of polymeric film layers to a plastic, metal or glass surface. These materials include starch based adhesives or casein based adhesives now predominantly used for glass applications since they do not bond well to plastic or metal. Specific adhesives that may be employed include EVA based materials which have free carboxyl groups, converted starch solutions, PVA based adhesives, casein based adhesives, synthetic resin dispersions for metal or plastic containers or blends of synthetic and starch based products and the like.
It is clear that one specific hydrophilic layer may not fit all applications but hydrophilic layers can be tailored to particular applications based on the conditions and requirements for wet PML labeling of polymeric substrates.
If an adhesion promoting tie layer or primer is employed to promote hydrophilic layer adhesion or adhesive adhesion, materials such as maleic anhydride, ethyl acrylic acid, carboxylated polyurethane resin and the like may be employed at levels of 0.1-3 1b/3,000 sq. ft.
If a cross-linking catalyst is added to the adhesion promoting tie layer, the ratio of catalyst to adhesion promoting tie layer may be an amount that is sufficient to cure the adhesion promoting tie layer. An excess of the catalyst, i.e. 5-25% in excess of the amount of the catalyst that is required to cure the adhesion promoting tie layer may be used to provide a portion of the catalyst at the interface of the adhesion tie promoter and the hydrophilic layer to increase the moisture resistance of the hydrophilic layer without decreasing the moisture absorbtivity of the hydrophilic layer. Additionally, excess catalyst can also be available to aid in curing of the adhesive.
Plasticizers such as n-di-octylphthalate may be employed at a level of 0.5-3% by weight of the adhesive composition to prevent the polymeric film label from losing flexibility.
The slip aids and anti-blocking compounds prevent excessive friction between the hydrophilic layer and the adhesive layer and also control the effect of ambient moisture levels which may tend to interfere with the operation of high speed automated machinery which is used for apply labels. These materials may be used at a level of 0.5-3% by weight of the hydrophilic composition or may be coextruded or coated with the low density film and include materials such as microcrystalline wax emulsions, erucamide disp, polytetrafluoroethylene compositions, silicone beads, modified silicone solutions, parafin wax emulsions, high melting polypropylene emulsions, carnauba wax emulsions, oxidized ethylene/EVA compositions, micronized polyethylene wax/PTFE emulsions, micronized polypropylene, micronized fluorocarbons such as PTFE (Teflon), micronized polyethylene, silica and talc.
If an antistatic agent is employed, it may be present at a level of 0.5-3% by weight of the hydrophilic formulation. These materials include quaternary ammonium salts such as Ethaquad C12, sulfonated styrene maleic anhydride, sulfonated polystyrene, sulfonated vinyl toluene maleic anhydride conductive polymers and organo modified silicones such as Silwet 77.
Protective coatings may be used to protect the exposed polymer film of the label when applied at a level of 0.25-4 lbs/3000 sq. ft. using conventional application techniques. These materials include styrenated acrylics such as OC1043 from O.C. Adhesives, Inc., Flexon Release Varnish from Manders-Premier.
If desired a humectant may be added to the hydrophilic layer at a level of 0.5-3% to provide curl resistance and to impart layflat properties to the polymeric film labels. These humectants include urea, polyethylene glycols (such as PEG400), polyvinyl alcohol, glycerine and the like.